In the electrophotographic process, various charging devices are needed to charge a photoreceptor (PR), recharge a toner layer, charge an intermediate transfer belt for electrostatic transfer of toner, or charge/discharge a sheet of media, such as a sheet of paper. Recent attempts for the charging devices have employed nanostructures (e.g., nanowires, nanotubes, nanorods, nanofibers and nanodots) as the electron emitting electrode contained in the subject charging device. For example, the charging devices may be a direct charging device including an emitter array of carbon nanotubes (CNTs) juxtapositioned and facing but spaced slightly away from the photoreceptor (PR). An electric bias is then applied between the CNT array and the PR to establish an electric field with the objective to initiate and sustain electron emission at the nanotube tips and to thereby generate and direct charges to the PR surface.
In another example, the charging devices may include one or more electrodes containing nano-structured arrays of electron emitting elements which may be employed as an indirect charging device that also employs a gas channel to create a high-speed gas stream impinging upon the photoreceptor. In this case, nano-structured arrays are configured inside the gas channel to generate charges that are captured on or within the gas molecules moving in the channel. The gas ions are then delivered to the PR surface by this high-speed impinging jet. Such indirect charging devices and their methods reduce the extrinsic contamination to the nano-structure array(s) and also provide a reduced device size which may result in an extreme reduction on the amount of waterfront on the receptor requiring direct access by the charger. Thus a smaller size printer, copier, fax, and/or multifunctional product may result.
Problems arise, however, because the delivery of charges to the photoreceptor relies on the gas stream in the gas channel, which generally requires high gas velocity (e.g., close to the speed of sound in air) as well as a high-density ion source (i.e., high space charge density) in order to deliver sufficient ions and charge to the photoreceptor. These requirements have proven to be a challenge to the widespread implementation of the indirect charging devices of the prior art.
Thus, there is a need to overcome these and other problems of the prior art and to provide an improved indirect charging system and method that can provide high charging performance operating with low velocity gas streams and low ion densities.